1. Field of the Invention
The present invention relates to a contact switch used for, for example, control of a high-frequency signal.
2. Description of the Related Art
With the improvement of an integration technique in recent years, size reduction, weight reduction, low voltage operation, low power consumption, and high frequency operation have been rapidly proceeded in electronic devices. In particular, in the technical field of a mobile communication terminal device such as a mobile phone, there is a demand for high performance in addition to the strictly-requested demands described above, and MEMS (micro electro mechanical system) has attracted attention as one of techniques to solve these contradictory issues. The MEMS is a system fusing a micro mechanical component and an electron circuit component by a silicon process technique. With the MEMS technique having excellent characteristics such as precision processability, it is possible to realize a compact and low-cost SoC (system on a chip), while responding to the high performance.
The MEMS technique is utilized in various fields, and is, for example, used for a switch mechanically performing coupling/decoupling of a signal line transmitting a high-frequency signal. In the switch for a high frequency signal, it is desirable to sufficiently reduce power loss (insertion loss) caused by insertion of the switch, and sufficiently improve insulating characteristics to ensure signal quality. A contact switch is cited as a switch satisfying these two characteristics at the same time, and it is utilized as an important component, in particular, in a circuit in which quality is strictly demanded. Further, the contact switch is also expected to be applied to a front-end circuit for high-speed large-capacity communication in a band carrier from a megahertz (MHz (106 Hz)) to a gigahertz (GHz (109 Hz)).
Many of the contact switches for the high frequency of the related art have a so-called series type contact structure because of easiness to ensure high isolation, and its wide application range on a circuit design. In the series type contact structure, for example, a signal line is mechanically coupled when a fixed contact point and a movable contact point forming a pair are in contact with each other (an on-state), and mechanically decoupled when they are not in contact with each other (an off-state).
In the switch using the series type contact structure, one of important factors influencing increase/decrease of the insertion loss is contact resistance in a contact section. Low insertion loss is realized as the contact resistance is low, so various techniques have been developed so far. The method most frequently utilized is a method reducing the contact resistance by providing a plurality of movable contact points to one fixed contact point to increase the number of contacts (multi-point contact) (for example, refer to Japanese Unexamined Patent Publication No. 2008-27812)
The contact structure of Japanese Unexamined Patent Publication No. 2008-27812 includes a fixed contact point formed on a substrate, a plurality of movable contact points provided in positions facing the fixed contact point in a cavity, and a movable beam holding these movable contact points. In this structure, the movable beam is displaced by an external drive circuit to switch a contact state and a non-contact state of the fixed contact point and the movable contact point, and this serves as a switch performing coupling/decoupling of the signal line. This contact structure (hereinafter, referred to as a multi-point contact structure) is easily manufactured, and is thus put into practical use in many switches.